Always return available for SyncClassView command

Merge release/dev16.4 to release/dev16.4-vs-deps

Merge release/dev16.4 to release/dev16.4-vs-deps

Don't crash on self-referencing attribute in nullable

Merge release/dev16.4 to release/dev16.4-vs-deps

* EnC: Use the current document encoding when reading source text from file.

* Optimization

Merge release/dev16.4 to release/dev16.4-vs-deps

* Update dependencies from https://github.com/dotnet/arcade build 20191205.2

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19605.2

* Pack Content for anlyzer packages

* Skip failing C# REPL integration tests.

After CI image was updated with 16.4 Preview 5 some REPL tests started
failing consistently. https://github.com/dotnet/roslyn/issues/40160

* Skip additional test

* EnC: Fix document out-of-sync checks when module is not loaded when debugging session starts

Previous change https://github.com/dotnet/roslyn/pull/39295 allowed us to rely on PDB source file checksums when distinguishing between design-time-only documents that should be ignored when applying changes and documents whose changes must be applied to the debuggee. The change did not handle the case when the PDB isn't loaded yet when this check is being performed. This bug resulted in changes not being applied correctly and documents getting out-of-sync in scenarios where the modules were not loaded to the debuggee fast enough.

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1013242

Merge release/dev16.4 to release/dev16.4-vs-deps

Fix stack overflow in inheritdoc evaluation

LOC CHECKIN | dotnet/roslyn  release/dev16.4-vs-deps | 20191101

Merge release/dev16.4 to release/dev16.4-vs-deps

The AnalyzerConfigSet had a race where we were storing the pooled object
in the cache. It turns out that this often works, due to hash codes mapping
different sets to different buckets, but is wildly unsafe and can produce
almost any result.

This change releases the object from the pool before using it as a key.

Fixes #39599

Don't try to use UIContexts if we are in a command line build

Do not report EnC diagnostics when EnC is disabled

This code isn't new, but the use inside VisualStudioWorkspaceImpl.cs
meant that we'd throw an exception when a project was added. This
would get caught by the project system and converted back to an
HRESULT.

Customer reports claim this is a regression in newer builds, and
I can't disagree with that but can't explain it. We have integration
tests that test this, and on our CI right now they are passing. I
similarly saw passing tests locally when I previously investigated this
but am now seeing failing tests on newer dogfood builds. I also saw
it fail once with a different error code or simply no error code; it
leads me to believe that something environmental can cause either the
HRESULT to be converted differently (as this is using IErrorInfo which
is often the cause of spooky-action-at-a-distance) or something
the project system is doing is swallowing the exception. It's
unclear but the fix seems the same no matter what.

Fixes https://developercommunity.visualstudio.com/content/problem/806929/command-line-builds-using-devenv-no-longer-work-fo.html

Merge release/dev16.4 to release/dev16.4-vs-deps

Merge release/dev16.4 to release/dev16.4-vs-deps

Switch some calls to ThreadHelper.ThrowIfNotOnUIThread to something else

Update release/dev16.4 version to -beta4

Merge release/dev16.4 to release/dev16.4-vs-deps

Revert "Run integration tests with .NET Core SDK shipped with VS"

Use resource strings for validating warning text

Skip failing integration tests

Merge release/dev16.4 to release/dev16.4-vs-deps

Fix crash where we are not always finding text snapshots